• Journal of Sensor Science and Technology
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• v.11 no.1
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• pp.1-8
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• 2002

In this paper, a thermopile which is applied to wide uses of temperature measuring was fabricated and its characteristic was improved by appling SOI structure to the fabrication. We improved characteristic of the thermopile by using single crystal silicon strips that has high seebeck coefficient and dielectric isolating the silicon strips from substrate with silicon dioxide film which dramatically decrease thermal conductivity between hot and cold junction compared to a silicon strip which was fabricated by ion implantation. The thermopile consists of 17 p-type single crystal silicon strips and 17 n-types by serial connection. The result of electromotive force measuring showed very good characteristic as 130mV/K when temperature difference between the two ends of the thermopile occurs by applying light on the thermopile fabricated with silicon strips of $1600{\mu}m$ length, $40{\mu}m$ width, $1{\mu}m$ thickness.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.1
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• pp.60-68
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• 2011

[ $ZrO_2-TiO_2$ ]binary oxides with various Zr:Ti molar ratios were prepared by sol-gel method and Nafion$^{(R)}$/$ZrO_2-TiO_2$ composite membranes were fabricated for proton exchange membrane fuel cells (PEMFCs) at high temperature and low humidity. Water uptake, Ion exchange capacity (IEC), and proton conductivity of Nafion$^{(R)}$/$ZrO_2-TiO_2$ composite membranes were characterized and these composite membranes were tested in a single cell at $120^{\circ}C$ with various relative humidity (R.H.) conditions. The obtained results were compared with the unmodified membranes (Nafion$^{(R)}$ 112 and Recast Nafion$^{(R)}$). A Nafion$^{(R)}$/$ZrO_2-TiO_2$ composite membrane with 1:3 of Zr:Ti molar ratio showed the highest performance. The performance showed 500 mW/$cm^2$ (0.499V) at $120^{\circ}C$, 50% R. H., and 2 atm.

• Journal of the Korean Chemical Society
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• v.33 no.5
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• pp.445-451
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• 1989

A series of solid solutions with formula $Er_{1-x}Sr_xFeO_{3-y}, where x is from 0.0 to 1.0, has been synthesized by heating at $1200^{\circ}C$ for 24 hours. X-ray diffraction shows these samples to be orthorhombically distorted perovskites for compositions up to x = 0. 6 and apparantly simple cubic perovskite structures from $0.8{\leq}x{\leq}1.0$. Lattice volumes are increased with the introduction of Sr. The mixed valence state of two kinds of Fe ion in these ferrite systems is analyzed by the Mohr salt titration method. Mossbauer spectra measured at room temperature for x = 0.0 and 0.5 compositions shows hyperfine splitting for iron (III) due to magnetic ordering and indicates that these samples contain octahedrally and tetrahedrally coordinated iron sites. Electrical conductivity measurements indicate that conduction in these samples apparantly occurs over the octahedral sites by a hopping mechanism.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1357-1368
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• 1995

Nasigels of composition Na0.75Zr2PSi2O12 and Na3Zr2PSi2O12 have been synthesized by the sol-gel technique using metal alkoxide precursors. The monolithic dry gels of Na0.75Zr2PSi2O12 with no crack have been prepared by the control of the shrinkage rte, but gels of Na3Zr2PSi2O12 were impossible to prepare without cracking. The gels treated up to 80$0^{\circ}C$ led to the formtion of glass but the glasses were converted to the crystalline phases at above this temperature. Crystaline phases precipitated from the Na0.75Zr2PSi2O12 glass were NASICON-like phase, Na2Si2O5, and free Zirconia. Phase that precipitated from the Na3Zr2PSi2O12 was only rhombohedral NASICON. For Na0.75Zr2PSi2O12 gels, framework of PO4 tetrahedra and SiO4(PO4) tetrahedra formed at low temperature but changed to that of SiO4 and SiO4(PO4) tetrahedras as it were crystallized. In the case of Na3Zr2PSi2O12 gel, framework of isolated PO4 and SiO4 tetrahedras formed at low temperature but changed to SiO4(PO4) tetrahedra framework which usually formed in the NASICON crystal after crystallization at high temperature. The gels treated up to 80$0^{\circ}C$ contained the residual water. The ionic conduction was attributed to the motion of proton and Na+ ion at low (up to 150~20$0^{\circ}C$) and high temperatures, respectively. As the temperature of heat treatment increased, ionic conductivity gradaully increased with the extent of precipitation of crystalline phase.

• Korean Journal of Materials Research
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• v.20 no.2
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• pp.55-59
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• 2010

$Na^+$ ion conductivity can be improved by the substitution of an Mg atom for an Al atom to form a nonstoichiometric $Na^+$ $\beta$-alumina. We performed a first principles study to investigate the most stable substitution site of an Mg atom and the resulting structural change of the nonstoichiometric $Na^+$ $\beta$-alumina. Al atoms were classified as four different layers in the spinel block that are separated by conduction planes in the nonstoichiometric $Na^+$ $\beta$-alumina. The substitution of an Mg atom for an Al atom at a tetragonal site was more favorable than that at an octahedral site. The substitution in the spinel block was more favorable than that close to the conduction plane. This result was well explained by the volume changes of the polyhedrons, by the standard deviation of the Mg-O distance, and by the comparison with bulk MgO structure. Our result indicates that the most preferable site for the Mg atom was the tetrahedral site at the spinel block in the nonstoichiometric $Na^+$ $\beta$-alumina.

• Journal of the Korean Chemical Society
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• v.36 no.2
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• pp.174-179
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• 1992

Reaction of aniline and iodine in$CHCl_3,\;CH_2Cl_2 : CHCl_3$(1 : 1), and $CH_2Cl_2$ has been studied kinetically by using conductivity method, Pseudo first-order rate constants ($k_{obs}$) and second-order rate constants ($k_{obs}$/[aniline]) are dependent on the aniline concentration. Second-order rate constants obtained were increased with increasing aniline concentration. We analysed these results on the basis of formation of charge transfer complex as reaction intermediate. From the construction of react ion scheme and derivation of rate equation, we calculated equilibrium constants and activation parameters for the formation and transformation of charge transfer complex. The equilibrium constants were decreased by an increase in the dielectric constant of the solvent and the value is 1.7-3.7$M^{-1}$. The rate of transformation are markedly affected by the solvent polarity. ${\Delta}H^{\neq}$ is about 14.2kJ/mol, and ${\Delta}S^{\neq}$ is large negative value of -243J/mol K.

• Korean Journal of Materials Research
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• v.17 no.4
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• pp.227-231
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• 2007

Transparent conducting indium tin oxide (ITO) films were deposited onto the Polyethersulfone (PES) substrate by using a magnetron sputter type negative metal ion source. In order to investigate the influence of cesium (Cs) partial pressure during deposition and annealing temperature on the optoelectrical properties of ITO/PES film the films were deposited under different Cs partial pressures and post deposition annealed under different annealing temperature from $100^{\circ}C$ to $170^{\circ}C$ for 20 min at $3\;{\times}\;10^{-1}$ Pa. Optoeleetrical properties of ITO films deposited without intentional substrate heating was influenced strongly by the Cs partial pressure and the Cs partial pressure of $1.5\;{\times}\;10^{-3}$ Pa was characterized as an optimal Cs flow condition. By increasing post-deposition vacuum annealing temperature both optical transmission in visible light region and electrical conductivity of ITO films were increased. Atomic force microscopy (AFM) micrographs showed that the surface roughness also varied with post-deposition vacuum annealing temperature.

• Membrane Journal
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• v.26 no.2
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• pp.146-151
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• 2016

Sulfonated poly (arylene ether sulfone) (SPAES) random copolymers have merits such as high proton conductivity, relatively low production cost, and thermochemical resistance when applied as polymer electrolyte membranes for fuel cells. However, it is difficult to directly employ SPAES copolymers into practical fuel cell membrane applications owing to their low chemical stability and dimensional instability under harsh operation conditions. A plausible solution is to impregnate SPAES copolymers into support films (e.g., electrospun polyimide support) with interconnected pore structures and high thermochemical toughness. In this study, a SPAES copolymer with a swivel group, which induces high free volume for fast ion transport, is chosen as ionomers to prepare pore-filling membranes (PFMs). The feasibility of the resulting membranes is evaluated via membrane characterizations.

• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.539-548
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• 2016

The non-noble 1D nanofibers(NFs) prepared by electrospinning and calcination method were used as oxygen evolution reaction (OER) electrocatalyst for water electrolysis. The electrospinning process and rate of solution composition was optimized to prepare uniform and non-beaded PVP polymer electrospun NFs. The diameter and morphology of PVP NFs changed in accordance with the viscosity and ion conductivity. The clean metal precursor contained electrospun fibers were synthesized via the optimized electrospinning process and solution composition. The calcined $CuCo_2O_4$ NFs catalyst showed higher activity and long-term cycle stability for OER compared with other $Co_3O_4$, $NiCo_2O$ NF catalysts. Furthermore, the $CuCo_2O_4$ NFs maintained the OER activity during long-term cycle test compared with commercial $CuCo_2O_4$ nanoparticle catalyst due to unique physicochemical and electrochemical properties by1D nanostructure.

• Journal of the Korean Electrochemical Society
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• v.18 no.3
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• pp.130-135
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• 2015

The rate capability and low-temperature characteristics of graphite electrode are investigated after surface treatment with copper phthalocyanine (CuPc) or phthalocyanine (Pc). Uniform coating layers comprising amorphous carbon or copper are generated after the treatment. The rate performance of graphite electrodes is enhanced by the surface treatment, which is more prominent with CuPc. The resistance of the graphite electrode estimated from electrochemical impedance spectroscopy and pulse resistance measurement is the smallest for the CuPc-treated graphite. It is likely that the amorphous carbon layer formed by the decomposition of Pc facilitates $Li^+$ diffusion and the metallic copper derived from CuPc improves the electrical conductivity of the graphite electrode.